Aquarium Water Change Calculator
About Water Changes
Removing (dirty) water from the aquarium and adding new (clean) water helps to reduce unwanted organic compounds and other nuisance compounds by dilution. However, most reef keepers have been lulled into a false sense of security regarding the actual effectiveness of using water changes to reduce or eliminate problematic substances in the aquarium. The volume and frequency of the aquarium water changes directly correlate to their effectiveness with regard to nitrate and phosphate (among other compounds) reduction.
I built this calculator when battling my "Old Tank Syndrome" problem and used it to help me understand why the water changes were doing little to bring my total phosphates down to a controllable level. While aquarium water changes are very important, it should become clear (after playing with the water change calculator) that water changes alone are not usually suitable as the sole means of nutrient export in the reef aquarium. Water changes can help to reduce (dilute) phosphate and other dissolved compounds but because they are also being continually added (see below) supplementary means of export (skimming, ATS, etc) MUST be incorporated or OTS is inevitable.
Water Change Calculator Use
Phosphate is in the food:
Assuming 75% rough estimate: